For some time the prior art has included machines in which, through a variously-shaped inlet, a liquid-solid mixture is introduced in which a transport organ, generally an Archimedes screw, rotates internally of a screen in order to transport the solid parts towards an outlet, while allowing the liquids to pass through the holes in the screen.
The solid parts arrive in proximity of the outlet, pushed by the transport organ, with a considerable amount of liquid still in them; it is therefore necessary to compact the material further in order to extract the greatest possible quantity of liquid therefrom, as well as to have as dry a material as possible exiting the machinery.
In order to perform this operation devices are generally used which are provided with heavy mobile walls which occlude the outlet and which are distanced therefrom, with an axial or rotary motion, by the material being pushed by the transport organ towards the outlet; the material which, in order to exit, pushes against the mobile wall and is compacted, the residual part of liquid still contained therein being removed.
The mobile walls in known devices, usually realised with metal sheets of various shapes, as well as being very heavy and therefore unwieldy also require connection systems to the machinery on which they are mounted, which systems must provide the guided movement of the mobile walls, generally in an axial direction or rotating about a fixed axis; levers of various types are therefore used to enable a distancing or nearing axial motion of the mobile wall from the outlet, or hinging systems to enable the mobile wall to be rotated, generally about an axis which is external of the outlet hole, from a position in which the mobile wall is facing the outlet to a position in which the mobile wall is raised by the outlet. The latter system, less complex than the former system, does not enable a homogeneous compaction of the material over the whole area of the outlet hole.
Further, all of the above-mentioned connection and movement systems constitute a complication and a cost increase in the construction of the devices; further, their maintenance and eventual replacement is neither easy nor rapid.